What is "Offset" in the fluid simulation "Bake" settings?
This is pulled from another link on baking. 

Simulate objects falling into water

original answer by gandalf3♦

The Offset just "offsets" the frames that are being read from the cache. 

Time: Note that baking always starts on frame 1, these settings control the behavior of the fluid (e.g. for slow motion effects)

Start: The number of seconds into the simulation to start caching data.

End: The simulation time of the scene End frame in seconds.

Offset: Number of frames to offset reading of the cache. This is the only setting which you can still change after baking.